This study on breast-feeding and its effects on health of the infant is based on assembled data of the Child Health and Development Studies. The approach of our studies is epidemiological and includes the evaluation of antecedents and determinants as well as of effects of breast-feeding. The relationships between demographic, sociocultural and personal variables of the mothers to adoption nd length of breast-feeding will be investigated. The health and development of infants who did not receive human milk will be compared with those who were breast-fed for less than one month, one to three months or for more than three months. We will compare frequency and types of illnesses in infacy and early childhood, weight gain and physical growth, and behavioral characteristics as expressions of mother-child interaction.